Retractable casting core box with elastomeric joint seal

ABSTRACT

A retractable core for use with an outer form in producing concrete castings includes a rectangular wall-forming box having a hollow interior and an opening at its bottom to allow access to its interior. The walls of the box are separated symmetrically into four quadrants, and the lines of separation between quadrants are sealed by a compressible elastomer. A retracting mechanism inside the box is connected to each quadrant. In use, concrete is poured over the box, and after the concrete cures, the retracting mechanism pulls each quadrant toward the center of the core to compress the elastomeric seal and thereby shrink the size of the core. The casting is then lifted over the core. Each quadrant is mounted on a separate set of elastically bendable support arms which deflect during retraction of the core and the subsequent return of the core to its initial wall-forming position.

United States Patent [191 Beemer et al.

June 4, 1974 l RETRACTABLE CASTING CORE BOX WITH ELASTOMERIC JOINT SEALPrimary Examiner-Robert D. Baldwin [75] Inventors. Paul K Beemer LagunaBeach Attorney, Agent, or FirmChristie, Parker & Hale a 9 a I gzrilfgeHuck, Fullerton, both of 57] ABSTRACT i A retractable core for use withan outer form in prol l Asslgneei Amel'olls -9 y Park, Callfducingconcrete castings includes a rectangular wall- [22] Filed: July 0, 1972forming box having a hollow interior and an opening at its bottom toallow access to its interior. The walls l PP -r 270,465 of the box areseparated symmetrically into four quadrants, and the lines of separationbetween quadrants [521 US. Cl 249/179, 249/152, 249/180, are Sealed ycompressiPle elastomer- A retracting 249/183 mechanism Inside the box ISconnected to each quad- 51 Im. Cl B28b 7/30 ram Concrete is Poured Overthe and [58] Field of Search 249/178-182, the concrete cures theretracting mechanism 249/183 152 153 173 each quadrant toward the centerof the core to compress the elastomeric seal and thereby shrink the size[56] References Cited of the core. The casting is then lifted over thecore.

Each quadrant is mounted on a separate set of elasti- UNITED STATESPATENTS cally bendable support arms which deflect during rel50,3334/1874 Leverty 242/183 X traction f the core and the Subsequent returnof the l core to its initial wall-forming position. 3:754:7I7 8/1973Daidla 249/180 X 16 Claims, 15 Drawing Figures -32 ii, 48 'i 35 64 I $2Q 7s 42 3 L s 44 6 120 J L 24) b2 66 l 30 ,1, 1/ I I20 I "-1.. Q: I //240 I ,4 g 442. 42 I 40 i 7 74 J8 l 1 t; I g

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\ rlllilllllii lllllllll l RETRACTABLE CASTING CORE BOX WITH ELASTOMERICJOINT SEAL BACKGROUND OF THE INVENTION This invention relates to the artof concrete casting, and more particularly to an improved retractableinner form or core for use in casting generally hollow concreteproducts.

In the art of casting generally hollow concrete products, wet concretetypically is poured over a wallforming retractable core. An expandableouter form is disposed around the outer periphery of the core, and thenatural force of gravity acts on the wet concrete to fill the spacebetween the outer form and the core. After the concrete cures, the outerform is removed, and the walls of the core are retracted so the castingcan be stripped from the core. Release and removal of the outer form isa relatively simple task, but considerable difficulty has beenexperienced in retracting the walls of the core and stripping thecasting from the core.

Generally speaking, prior art casting cores include relatively complexretracting mechanisms for collapsing both sides and both ends of thecore. Such retracting mechanisms are expensive, require a great deal oflabor and time to operate, and generally require substantial maintenancecosts.

The prior art casting cores generally include several retractable wallsections which interfit to form the inner wall surfaces of the core.Some prior art casting cores include retractable corner sections whichinterfit with separate retractable side and end wall sections. A chiefdisadvantage of these prior art devices is that wet concrete permeatesthe joints between the interfitting wall sections. The concrete hardensin the joints as the casting cures. This makes it difficult to removethe core from the casting and to clean the core afterwards. Moreover,the joints create irregularities in the interior surface of the casting,which requires considerable hand grinding or filling with grout toproduce a smooth cast product.

SUMMARY OF THE INVENTION This invention provides a retractable castingcore which is relatively simple in construction and operation, and haslow production and maintenance costs.

Briefly, the retractable core includes wall-forming means having anouter surface shaped to define the contour of the hollowed interior of aconcrete casting. The wall-forming means includes movable wall sectionsarranged to form a hollowed interior. A compressible elastomer seals thespace between the wall sections. The hollowed interior of the corehouses retracting means connected to each wall section. The wallretracting means are operative to apply a force on each wall section ina direction to move the wall section so as to compress the joint sealand allow the wall sections to retract inwardly from the hollowedinterior of the concrete casting. The casting can then be lifted overthe core. 1

The elastomeric seal avoids the prior art use of complicated mechanismsto retract inter-fitting wall panel sections. The wall sections of thethis invention are retracted simultaneously by a simple retractingmechanism of suitable design. Moreover, the joint seal provides animpervious barrier to fluidous concrete which contacts the core, theeliminates the problem of such concrete permeating joints between wallsections of the core.

In a preferred form of the invention, the wall-forming means is shapedas a hollowed rectangular box to form a rectangular hollowed area in thecasting. The box preferably has an opening in its bottom for access toits interior. The box is separated substantially symmetrically into fourquadrants, and the lines of separation between quadrants are sealed bythe compressible elastomer. A separate retracting arm is connected tothe interior of each quadrant, and as the arms are retracted in unisontoward the center of the box, the quadrants apply a substantiallyuniform compression force on the seal and thereby collapse substantiallyuniformly from the interior of the casting. Alternately, the retractingmechanism can be separate activators adapted to bridge certain parts ofthe seal and be retracted to squeeze the seal substantially uniformlythroughout its length.

A preferred seal is configured so that pressure applied by theretracting walls of the core is directed at a point eccentric to thecentroid of theseal to prevent the seal from bulging beyond the outersurfaces of the core. Thus, the seal offers no resistance to theconcrete casting when the casting is removed from the core. Thisprevents the seal from being worn away and thereby formingirregularities in the inner wall of the cast product.

BRIEF DESCRIPTION OF THE DRAWINGS These and other aspects of theinvention will be more fully understood by referring to the followingdetailed description and the accompanying drawings, in which:

FIG. 1 is a schematicelevation view showing a retractable casting coreduring casting operations;

FIG. 2 is a schematic perspective view showing the casting core and anelastomeric seal between wall sections of the core;

FIG. 3 is a sectional plan elevation view taken on line 3-3 of FIG. 2;

FIG. 4 is a fragmentary sectional elevation view taken on line 4-4 ofFIG. 2;

FIG. 5 is a fragmentary schematic sectional elevation view showing thecross-sectional shape of the elastomeric seal prior to retraction of thewall sections of the core;

FIG. 6 is a fragmentary schematic sectional elevation view showing theseal of FIG. 5 at an intermediate stage of the retracting operation;

FIG. 7 is a fragmentary schematic sectional elevation view showing thejoint seal of FIG. 5 at a final stage of the retracting operation;

FIG. 8 is a fragmentary elevation view, partly in section, showing theconfiguration of the elastomeric seal at a corner of the core prior toretraction of the wall sections of the core;

i FIG. 9 is a fragmentary elevation view taken on line 9-9 of FIG. 8;

FIG. 10 is a fragmentary elevation view, partly in section, showing thecomer section of the seal of FIG. 8 at a final stage of the retractingoperation;

FIG. 11 is a fragmentary elevation view taken on line 11-11 of FIG. 10;

FIG. 12 is a sectional elevation view showing an alternate embodiment ofa compressible joint seal;

FIG. 13 is a sectional elevation view showing a further alternateembodiment of a compressible joint seal;

FIG. 14 is a fragmentary plan elevation view, partly in section, showingalternate retracting means in the case of FIG. 1; and

FIG. 15 is a sectional elevation view showing an alternate retractablecasting core for use in making concrete pipe.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1and 2, a concrete mold assembly 12 forms a generally hollow pre-castconcrete product 13. A presently preferred use of mold assembly 12 is inthe manufacture of pre-cast modular building units, such as steelreinforced concrete rooms for use in construction of multi-storydwelling units, such as hotels, town houses, and apartments. However,the invention can be applied to the manufacture of a variety of othercast concrete products, particularly generally hollow products ofrectangular configuration, such as septic tanks, burial vaults, and thelike.

The present invention is directed to a generally rectangular retractablecasting core 14 which forms the hollowed interior of casting 13. Thecore is supported on a set of upright supports arms 16 which are made ofresilient spring steelto allow them to deflect slightly, as described indetail below. I

A horizontally disposed pallet 18 spans the outer perimeter of the coreat a level continuous with the base of the core. The pallet is supportedon upright piers 20. The outer perimeterof the pallet is enclosed by anexpandable outer form which includes a pair of opposed upright end wallsections 20 spaced from the end walls of the core, and a pair of opposedside wall sections (not shown in FIG. 2 for clarity) spaced from theside walls of the core. The ends of the side wall sections are-joinedwith the ends of end wall sections 20 so the outer form provides arectangular, hollow, box-like wall-forming apparatus which encompassesthe outer perimeter of the pallet.

The outer form and the core combine to form a rectangular mold intowhich wet concrete is poured to form concrete product- 13. After theconcrete cures, the outer form is removed from the casting. Each endwall section 20 is mounted on an upright support 241 which facilitatesmovement of the end wall section from the casting. The side wallsections of the outer form are mounted on identical movable uprightsupports (not shown for clarity).

After removal of the outer form, the casting is stripped from the core.In accordance with the present invention, core 14 is retracted and theconcrete casting is then lifted over the core.

Construction of core 1 .4 is understood best by referring to FIGS. 2, 3,and 4. The core comprises a generally rectangular box having an opening26 in its bottom to allow access to its interior. The end walls and sidewalls of the box are each-divided in half, and the top of the box isdivided into four equal parts, with the lines of separation dividing thebox symmetrically into four equal quadrants'28. Each quadrant is aseparate wallforming corner section having a separate end wall section30, side wall section 32, and top panel section 34.

Each quadrant is mounted on a separate set of the support arms 16.

The space between quadrants is sealed by a narrow compressibleelastomeric joint seal 36. The joint seal follows the lines ofseparation of the box. Thus, it is X- shaped when the box is viewed inplan view, and it follows the vertical centerline of each side wall andend wall of the box.

The bottom of each side wall and end wall has a separate horizontallydisposed ridge 40 projecting into the interior of the box to define amarginal lip which encompasses the lower interior portion of the box.The lip defines the substantially elliptical-shaped perimeter of opening26. Each ridge 40 is separated from its adjacent ridges to allow roomfor each quadrant to move relative to the others. A pair of holes 42extend through the two end portions of each ridge, and a separate hole44 extends through'the corner portion of each ridge. The tops of supportarms 16 extend through holes 42 and 44 to support the inner core in itsoperative position during casting of the concrete.

A separate marginal groove 46 is formed in each edge of each quadrant.Grooves of adjacent quadrants are disposed side-by-side and cooperate tohold the joint seal in place. As shown best in FIGS. 3 and 4, the sealhas a pair of opposed outwardly projecting elongated shoulders 48 alongits sides. The shoulders are fitted into corresponding grooves in eachpair of adjacent quadrants. When the core is in its casting position(shown in FIGS. 3 and 4) in readiness for pouring of the concrete, theseal is maintained in a non-bulging condition, with its outer surface 50flush with the outer surfaces of the quadrants.

The shoulders make a tight friction fit in their corresponding grooves.Prior to use of the core, the wall sections of the quadrants aeretracted inwardly toward the center of the core to an operating pointat which a slight pre-compression force is constantly applied to theseal. FIGS. 3 and 4 show the seal at its operating point in readinessfor pouring of the concrete. The seal is maintained in a non-bulgingcondition, with its outer surface 50 flush with the outer surfaces ofthe quadrants. The pre-compression force prevents the cement slurry frompenetrating the area between the seal and the edge of each wall section.I

In use, after the concrete casting 13 has cured, the walls of the coreare retracted inwardly from the interior of the casting to allow thecasting to-be lifted over the core. The core is retracted by aretracting mechanism in the interior of the core. The retractingmechanism can take a variety of forms without departing from the scopeof the invention. Preferably, the retracting mechanism applies aretracting force to the corner of each quadrant to compress joint seal36 substantially uniformlyalong its entire length. Thus, each end wallsection 30 and side wall section 32 of each quadrant moves inwardly asubstantially uniform distance from corresponding interior walls of thecasting. This allows the casting to be easily slipped over the top ofthe core.

Joint seal 36 is made of a non-porous, compressible elastomer, such as asynthetic rubber. The preferred elastomer is of 40 to Shore A Durometerhardness, oil resistant neoprene. Such a material is rugged during use,and is thus able to withstand the constant compression and expansion towhich it is subjected. It is also impervious to attach by the cementwith which it comes in contact. Porous or sponge rubber is not desired,because it is not rugged, and the pores of such material becomepermeated with the cement slurry, which would cause the seal toeventually break down in use. The preferred non-porous hard rubberelastomer is substantially volumetrically incompressible, i.e., thejoint is resilient, or deformable, but its volume remains substantiallyconstant when it is deformed. Thus, the joint bulges when compressedbetween the edges of the wall sections.

The cross-sectional configuration of the seal is such that a majorportion of its mass is located inwardly of the axis on which pressure isapplied by the adjacent wall sections. This configuration prevents outersurface 50 of the seal from bulging beyond the outer surfaces of thewalls of the core when compressed. A bulging elastomer would be abradedaway by the interior side walls of the concrete casting when it islifted over the top of the inner core. Thus, the outer surface 50 of theelastomer soon would take a concave shape during subsequent moldingoperations with wet concrete. An inwardly projecting convex ridge wouldthus be formed in the center of all four inside walls of the casting,which would require considerable hand grinding to remove.

The remaining characteristics of the joint seal are described in detailbelow.

FIGS. 3 and 4 show a presently preferred retracting mechanism, whichincludes a vertically extending hydraulic cylinder 52 aligned with thevertical centerline of the interior of the core. A swivel-mounted upperspi der 54 is at the top of the cylinder, and a swivelmounted lowerspider 56 is at the bottom of the cylinder. The upper and lower spidersare shown in their fully extended positions positioning the walls of thecore in their operative positions in preparation for molding operations.

Upper spider 54 includes a pair of horizontally disposed and radiallyextending, elongated fixed retraction arms 58 extending to the cornersof a pair of quadrants on one side of the inner core, and a second pairof horizontally disposed and radially extending elongated adjustableretraction arms 60 extending to the corners of the two quadrants on theother side of the core. Arms 5 8 and 60 are the same elevation. Theouter ends of each arm 58, 60 carries a respective fixed yoke 62 whichfits around a respective bracket 64 at the corner of each quadrant. Eachyoke is secured to the bracket by a separate transverse pivot pin 66 sothe outer ends of the retraction arms 58, 6t) swivel about theirrespective brackets.

The inner end of each retraction arm 58, 60 carries a respective fixedyoke 68 which fits around a respective radially extending fixed bracket70rigidly secured to a fixed annular collar 72 at the top of hydrauliccylinder 52. Each yoke 68 is secured to its corresponding bracket 70 bya respective transverse pivot pin 74, so the inner end of each arm 58,60 is able to pivot relative to its corresponding bracket.

The inner and outer ends of each adjustable arm 60 have correspondingexternally threaded shank portions 76, 78, respectively. The outer endof each shank threads into a corresponding internally threaded portionof outer yoke 62, and the inner end of each shank threads into acorresponding portion of inner yoke 68. Thus, the effective length ofretraction arms 60 is adjustable, which enables the retraction arms ofthe upper spider to be set at the same effective length as those of thelower spider, and provides means for adjusting the amount ofpre-compression force of the joint seal. Moreover, the adjustmentfacilitates mounting of the upper spider in the interior of the core-Hydraulic cylinder 52 includes a vertically extending and contractablepiston arm at its top. A fitting 82 rigidly coupled to piston arm 80carries collar 72. Thus, extension of piston arm 80 drives the collarup, which causes retraction arms 58, 60 to swivel at their ends and moveupwardly to the diagonal position shown in phantom lines in FIG. 4.

The hydraulic cylinder is suspended within the core by a pair ofupwardly extending chains 84 reeved over corresponding horizontallydisposed drums 86 mounted in the upper interior portion of the core. Thechains extend downwardly from the drums to a point where they are fixedto hold the cylinder at an elevation which maintains arms 58, 60 in asubstantially horizontal position during casting operations. A singlechain 88 extends downwardly from the bottom of the cylinder 52 to apoint where it is fixed so as to maintain the cylinder in a fixedposition in the interior of the core.

Lower spider 56 includes a pair of radially extending and horizontallydisposed fixed retraction arms 90 secured to corners of a pair ofquadrants, and a pair of radially extending and horizontally disposedadjustable retraction arms 92 secured to comers of the other pair ofquadrants. Fixed arms 90 are identical in construction to those of upperspider 54. Their outer ends are pivotally mounted to separate brackets94 secured to the corners of the quadrants. The inner ends of fixed arms90 are mounted to swivel about a radially extending bracket 96 fixed tothe bottom of hydraulic cylinder 52.

Adjustable arms 92 are identical in construction to those of upperspider 54. Their outer ends are pivotally mounted to separate brackets98 secured to the comers of the quadrants. The inner ends of theadjustable arms are mounted to swivel about separate radially extendingbrackets 100 fixed to the bottom of cylinder 52. The inner and outerends of adjustable arms 92 have corresponding externally threaded shankportions 102, 104, respectively, to facilitate adjustment of the arms.The lower spider also includes four radially extending and horizontallydisposed orthogonal retraction arms extending outwardly in mutuallyperpendicular directions from the bottom of cylinder 52. Orthogonalretraction arms 105 are located immediately above retarction arms 90,92. The ends of the orthogonal retraction arms bridge the four joints inthe outer walls of the quadrant to provide stiffness for the bottom ofthe core. The inner end of each arm 105 includes a yoke 106 fittedaround a respective radially extending fixed bracket 107 secured to thelower portion of cylinder 52. Each yoke is secured to the bracket by aseparate transverse pivot pin 108 so the inner ends of arms 102 canswivel about their respective brackets. Each yoke 106 has a separateexternally threaded shank portion 110 threaded into an internallythreaded portion in the inner end of the arm to facilitate adjustment ofthe effective length of the arms.

The outer end of each arm 105 is fitted between a corresponding pair ofinwardly projecting brackets 112. The pair of bracekts associated witheach arm are rigidly fixed to the interior walls of an adjacent pair ofthe quadrants. A separate transverse pivot pin 114 pivotally mounts theouter end of each arm between its corresponding brackets.

The joints at the bottom of the core are stiffened by separatestiffening assemblies 116. Each stiffening assembly includes a pair ofbrackets 118 rigidly secured chains 84 are initially adjusted to fix theelevation of I the hydraulic cylinder so that the arms of the upper andlower spiders are in a horizontal plane (as shown in FIG. 4) inreadiness for casting operations. The bottom chain 88 is fixed to holdthe hydraulic cylinder in a fixed vertical position.

After the casting has cured, and the outer form is removed, the innerform is retracted by initially pressurizing hydraulic cylinder 52. Thiscauses the piston arm 80 to extend upwardly, and also causes a lowerportion of the cylinder to move downwardly. This movement ofthe-cylinder drives arms 58, 60 of the upper spider upwardly to theposition shown in phantom lines in FIG. 4, and also drivesarms 90, 92,102 of the lower spider downwardly to the position shown in phantomlines in FIG. 4. This movement of the hydraulic cylinder shortens theeffective length of the upper and lower spiders to pull the side and endwalls of the core inwardly. The entire length of the elastomeric jointseal is squeezed substantially uniformly as the walls of the core areretracted, so that all walls of the core are retracted substantially thesame distance. A l-inch stroke of the hydraulic cylinder pulls the wallsinwardly about %thS of an inch, which is sufficient to allow the castingthe clear the outer walls of the core when lifted over the core.

The major portion of the body of the joint'seal bulges toward theinterior of thecore during retraction of the side walls, and its outersurface 50 moves inwardly to a slight concave curvature. Thus, the seal'is not abraded away when castings are lifted over the core.

After the casting is removed, the piston arm of the hydraulic cylinderis contracted to move the arms of the upper and lower spiders to theirinitial horizontal positions. Thismoves the outer walls of the core backto their operative positions in readiness for the next castingoperation.

Referring to FIGS. 5 through 7, the geometric crosssectionalconfiguration of the preferred joint seal 36 prevents the seal frombulging beyond the exterior of the wall sections when the seal issqueezed by the wall sections. The cross-sectional configuration of theseal includes a minor portion I26 which is confined betweenpressure-applying edges of the wall sections, and a major portion 128which protrudes toward the inter ior of the core and therefore away fromthe inner wall of casting 12.

The confined minor portion 126 has opposed short outer edges 130 whichproject away from shoulders 48 and intersect the non-bulging outersurface 50 at the corners of the seal. Edges 130 are compressed betweencorresponding pressure-applying edges 132 of the wall sections. Theminor portion 126 also includes shoulders 48, which are disposed in thepressure-applying grooves 46 of the wall sections, and the portion ofthe seal between the shoulders.

The protruding major portion 128 has outer edges 134 which are spacedfrom corresponding adjacent nonpressure-applying edges 136 of the wallsections. The spacing between edges 134 and wall section edges 136 issuch that even when the seal is compressed to its maximum amount, asshown in FIG. 7, edges 134 of the seal are substantially prevented fromcontacting edges 136 of the wall sections. The purpose of this result isdescribed in detail below.

FIGS. 5 through 7 show schematic views of the crosssectional area of thejoint seal, in which grid lines I38 on the seal illustrate the flowcharacteristics of the rubber in the seal when the seal is compressedfrom its initial casting position (FIG. 5), through an intermediateposition (FIG. 6), to a final stage (FIG. 7) in which maximum pressureis applied to the seal by the wall sections. When the wall sections areretracted, they apply pressure at a point eccentric to the centroid ofthe seal. The eccentric loading is on the side of the centroid occupiedby concrete casting 12, and this eccentric loading causes the rubber inthe seal to flow toward the protruding major portion 128 of the seal.This prevents the seal from bulging beyond. the plane of the outersurfaces of quadrants 28. Grid lines 138 become distorted when the sealis compressed, and thereby illustrate these flow characteristics of therubber in the seal.

When eccentric loading is applied, a non-uniform internal pressuredistribution builds up in the seal. The rubber in the confined minorportion of the seal experiences a relatively high pressure build-upduring such loading. The rubber in the protruding major portion 128 ofthe seal is a freely flowable' mass, and the internal pressure build-upin this area is relatively low during loading. Thus, the rubber in minorportion 32 flows to the low pressure zone of the seal during loading.The distorted grid lines show how this mass flow takes place. The rubberin the confined high pressurearea of the seal must flow somewhere whenloading is applied, and the eccentric loading directs the flow of rubberin the confined pressure receiving area toward the protruding lowpressure area of the seal. Since the latter portion of the seal is afreely flowable mass, it is capable of accepting the mass of rubberflowing from the eccentrically loaded area of the seal. Thus, as theminor portion 126 becomes progressively squeezed between thepressure-applying edges of the wall sections, the protruding portion ofthe seal progressively expands in size to accommodate the mass flow fromthe squeezed portion of the seal.

Thus, the eccentric loading of the seal induces flow away from the innerwalls of the concrete casting l2, and therefore prevents outer surfaceof the seal from bulging beyond the outer surfaces of the wall sectionsof the core.

As explained previously, the protruding major portion of the seal isshaped so its edges are prevented from coming into contact with theadjacent inner edges of the wall sections when the wall sections areretracted their maximum amount (shown in FIG. 7). If the walls come incontact with protruding portion 128, internal pressure will build up inthe protruding major portion, which would then inpair its free flowcharacteristics. This would prevent the protruding portion from freelyaccommodating the rubber flowing from the pressurereceiving minorportion, and could cause at least a portion of outer surface 50 to bulgebeyond the planeof the wall sections.

When the seal is squeezed between the wall sections, protruding portion128 expands volumetrically. Thus, lengthwise expansion of this portionof the seal must be accommodated at the corners of the inner core. FIGS.8 through 11 show a preferred method of accommodating lengthwiseexpansion. A pair of slotted areas 140 are formed in protruding portion128 near the corners of the core.

As shown best in FIG. 10, lengthwise expansion of protruding majorportions 128 fills the spaces provided by slotted areas 140. Thisprevents internal pressure build-up in the protruding portion of theseal, and thereby maintains the free flow characteristics of the seal toprevent the seal from bulging beyond the plane of the wall sections.

While the construction of the seal shown and described above is apreferred one, we contemplate that, alternately, compressible jointseals of other shapes and composition can be used in place of seal 36without departing from the scope of the invention. FIG. 12 shows analternate joint seal 142 which is rectangular in crosssection, and madeof a compressible elastomer such as neoprene. A separate elongated metalattaching strip 144 is bonded to each side of the seal. The attachingstrips are tapped for screws 146 for use in securing the attachingstrips to corresponding L-shaped brackets 148 on opposite sides of thespace between wall sections. I

FIG. 13 shows a compressible seal 150 which is retangular incross-section, and includes a major portion 152 of sponge rubber, with aperipheral strip 154 of sheet rubber covering the outer surface and bothsides of major portion 52. Preferably, the sheet rubber strip is made ofrelatively hard neoprene. The sides of the sponge rubber portion arerecessed to receive opposed metal attaching strips 156 which are tappedfor screws 158 for use in securing the attaching strips to brackets 148.

In use, both seal 142 and seal 150 bulge beyond the outer surfaces ofthe adjacent wall sections during compression, but in many applications,such as in the casting of concrete vaults or the like, such bulging maynot be undesirable. Moreover, each seal is relatively easilyreplaceable, and therefore new seals can besubstituted whenever abrasionbecomes excessive.

It is contemplated that, alternately, a variety of retracting means maybe used to retract the wall sections of the core without departing fromthe scope of the invention. As described above, it is preferred toretract the walls of the casting core by pulling inwardly on the cornerof each quadrant. The retracting mechanism shown in FIGS. 3 and 4 can bemodified, for example, by connecting the upper and lower spiders to arigid centrally disposed vertical rod (not shown), and then twisting therod on its axis by retracting suitably positioned hydraulic cylinders(not shown) coupled to the rod so the spiders pull the walls of the coreinwardly and compressthe seal.

FIG. 14 shows an alternate retracting device 160 to be used forretracting the walls of casting core 14. The retracting device shown inFIG. 14 extends across a portion of the seal at the joint between twoadjacent top panels 34 of the core. Retracting device 160 includes ahydraulic cylinder 162 with a retractable piston arm 164 bridging aportion of seal 36 inside the core. The hydraulic cylinder is rigidlysecured to one side of the seal, preferably by threading it into aninternally threaded bore 166 in an elongated gate member 168 extendingalong one side of the space between adjacent wall sections. The end ofthe piston arm extends through an opening 170 in a gate member 172 onthe other wall section, and is coupled to a fitting 174 joined to anelongated fixed rod 176 extending the length of the seal.

Preferably, several such retracting devices bridge the bottom, top, andintermediate portions of each vertical leg of the seal shown in FIG. 2,and several such retracting devices also bridge inner and outer portionsof each horizontal leg of the seal shown in FIG. 2. All hydrauliccylinders are suitably coupled to a central hydraulic system (notshown), and the walls of the core are retracted by pressurizing thecylinders in unison to retract their respective piston arms, and therebycompress the seal substantially uniformly along each of its vertical andhorizontal legs.

While the rectangular casting core 14 described above is a preferred useof the present invention, we contemplate that other retractable castingforms can be used in accordance with the present invention. For example,FIG. 15 shows a mold assembly 178 used in the vertical method of makinga concrete pipe 180. The mold assembly includes a vertically disposed,cylindrical outer form or shell 182, and a cylindrical inner form orcore 184 disposed concentrically inside the outer form. Outer form 182has a longitudinal split 186, and the split is sealed by a suitableelastomeric seal 188 disposed between opposed L-shaped flanges 190rigidly secured to opposite sides of the split. The flanges arereleasably secured together along the length of the split by suitablelongitudinally spaced apart fastening means, such as bolts 192.

The inner form has a longitudinal split 194 which is sealed byelastomeric joint seal 36. Preferably, seal 36 has an arcuately curvedouter surface 196 which is continuous with the circumference of theouter surface of the inner form. Shoulders 48 of the seal are seated inlongitudinally extending opposed slots 197 formed between the interiorwall of the inner form adjacent the split and opposed recessed portionsof a pair of gate members 198 extending the length of the inner formalong both sides of the split.

The inner form is retracted by a suitable retracting mechanism whichbridges gate members 198. By way of example, FIG. 15 shows a retractingmechanism which includes an L-shaped crank arm 200, the corner of whichis pivotally secured to an apertured lug 202 rigidly secured to one gatemember, and a lever arm 204 having one end pivotally secured to a lug206 on the other gate member. The other end of lever arm 204 ispivotallysecured to the crank arm leg which bridges the seal.Preferably, several such retracting mechanisms are spaced apart alongthe length of the-seal. An elongated rod 208 extending the length of theform is welded to the free end of each crank arm and in use, the rod isrotated, by suitable drive means (not shown), in the direction of thearrow in FIG. 15 to pivot the crank arms, and move the gate memberstoward each other to compress the seal and thereby retract the innerform.

I claim:

1. A retractable casting core for use with an outer form in the castingof generally hollow concrete products, the casting core comprisingwall-forming means in the form of a hollowed rectangular box having anouter mold surface which forms the contour of a hollowed interior of aconcrete casting, the outer mold surface of the wall-forming means beingseparated into wall sections cooperating with each other to form thecontour of the concrete casting interior, the wall-forming means havingone open end for access to a hollowed interior portion of theretractable casting core, the box being spearated substantiallysymmetrically into four quadrants with a compressible elastomeric'jointseal being disposed along each line of separation between the quadrants,and means in the hollowed interior portion of the casting core forapplying a force to retract each of the wall sections inwardly away fromthe interior of the casting, the wall retracting means directing acomponent of its retracting force in a direction transverse to the jointseal which borders each wall section to compress the seal to allow thewall sections to move toward each other as they move inwardly from theinterior of the casting, the retracting means also directing a componentof its retracting force in a direction eccentric of the centroid of theseal such that the seal is substantially prevented from bulging beyondthe outer surface of the wall sections.

2. Apparatus according to claim 1 in which the elastomeric seal is madeof a non-porous elastomer.

3. Apparatus according to claim 1 in which the elastomeric seal issubstantially volumetrically incompressible.

4. Apparatus according to claim 1 in which the wall retracting meanscomprises at least one elongated retraction arm connection to eachquadrant, and means for retracting each retraction arm.

5. Apparatus according to claim 1 in which each quadrant includes anupstanding end wall, an upstanding side wall which meets the end wall toform an upright corner of the box, and a toppanel above the side walland end wall.

6.Apparatus according to claim 5 in which each wall retractingmeanscomprises a separate elongated retraction arm connected to the uprightcorner of each quadrant, and means for retracting each arm.

7. Apparatusaccording to claim 5 in which the retraction arms comprise aspider arrangementcrossing at the central axis of the interior of thebox, each arm being mounted to swivel about a horizontal axis, and inwhich the retraction arms are located in the upper interior portion ofthe box, and a second set of retraction arms, each of which arms isconnected to an upright cornerof a respective quadrant, the'arms in thesecond set being in a spider arrangement so that they cross at thecentral axis of the interior of the box, and are disposed in the lowerinterior portion of the box, and including an extendable andcontractable, vertically extending arm disposed on the central axis ofthe interior of the box and connected between the first and second setsof spiders, whereby extension and contraction of the vertical arm pullsthe upper and lower spiders inwardly to retract the quadrants of theinnercore.

8. Apparatus according to claim 1 in which each wall section is mountedon a separate set of elongated movable supports.

9. A retractable casting core for use with an outer form in the castingof generally hollow concrete products, the casting core comprisingwall-forming means having an outer surface for forming the contour of ahollowed three-dimensional interior of a concrete casting, thewall-forming .means having a side portion which forms a closed moldsurface and is defined by intersecting first and second planes, and atop portion forming a mold surface which is integral with the sideportion and is defined by a third plane which intersects the first andsecond planes so the combined side-portion and top portion of thewall-forming means provide a continuous three-dimensional mold surface,the top and side portions being separated into wall sections cooperatingwith each other to form the contour of the concrete casting interior,the wall sections cooperating to form a hollowed interior area of theretractable casting core, a compressible elastomeric joint seal betweenthe wall sections, and means in the hollowed interior area of thecasting core for applying a force to retract each of the wall sectionsinwardly away from the interi or' of the concrete casting, the wallretracting means directing a component of its retracting force in adirection transverse to the joint seal which borders each wall sectionto compress the seal to allow the wall sections to move toward eachother as they move inwardly from the interior of the casting.

10. Apparatus according to claim 9 in which the wallforrning means isshaped as a hollowed rectangular box,

with one open end for access to a hollow interior of the box, and inwhich the box is separated substantially symmetrically into fourquadrants, the joint seal being aligned with each line of separationbetween the quadrants.

11. Apparatus according to claim 10 in which the wall retracting meanscomprises at least one elongated retraction arm connected to eachquadrant, and means for retracting each retraction arm.

12. Apparatus according to claim 10 in which the wall-forming means isengaged with the joint seal to direct a component of its retractingforce in a direction eccentric to the centroid of the seal such that theseal is substantially prevented from bulging beyond the outer surface ofthe quadrants.

13. A retractable casting core for'use with an outer form in a concretemold assembly, the retractable casting core comprising wall-formingmeans for providing an outer surface to form the contour of a hollowedthree-dimensional interior of a concrete casting, the wall-forming meansbeing divided into a plurality of separate wall sections havingcooperating outer surfaces which forrn the three-dimensional contour ofthe concrete casting interior, the wall sections cooperating to form ahollowed interior portion of the casting core, the separate wallsections being spaced apart from one another to define a plurality oflines of separation spaced around the wall-forming means, a compressibleelastomeric joint seal disposed in the lines of separation between theseparate wall sections, and means in the hollowed interior portion ofthe casting core for applying a retracting force to the wallsections tomove each wall section relative to the other wall sections inwardlywardly from the interior of the casting.

14. Apparatus according to claim 13 in which the retracting means alsodirects the component of its retracting force eccentric to the centroidof the seal such 13 14 that the seal is substantially prevented frombulging be- 16. Apparatus according to claim 15 in which at least Y theOuter Surface of the Wall Secnonsone elongated retracting arm isconnected to each wall 15. Apparatus according to claim 13 in which thewall sections are symmetrically arranged around the retractable castingcore, and in which the retracting 5 "8 arms In means retract the wallsections in unison.

section, and including means for retracting the retract-

1. A retractable casting core for use with an outer form in the castingof generally hollow concrete products, the casting core comprisingwall-forming means in the form of a hollowed rectangular box having anouter mold surface which forms the contour of a hollowed interior of aconcrete casting, the outer mold surface of the wall-forming means beingseparated into wall sections cooperating with each other to form thecontour of the concrete casting interior, the wall-forming means havingone open end for access to a hollowed interior portion of theretractable casting core, the box being spearated substantiallysymmetrically into four quadrants with a compressible elastomeric jointseal being disposed along eacH line of separation between the quadrants,and means in the hollowed interior portion of the casting core forapplying a force to retract each of the wall sections inwardly away fromthe interior of the casting, the wall retracting means directing acomponent of its retracting force in a direction transverse to the jointseal which borders each wall section to compress the seal to allow thewall sections to move toward each other as they move inwardly from theinterior of the casting, the retracting means also directing a componentof its retracting force in a direction eccentric of the centroid of theseal such that the seal is substantially prevented from bulging beyondthe outer surface of the wall sections.
 2. Apparatus according to claim1 in which the elastomeric seal is made of a non-porous elastomer. 3.Apparatus according to claim 1 in which the elastomeric seal issubstantially volumetrically incompressible.
 4. Apparatus according toclaim 1 in which the wall retracting means comprises at least oneelongated retraction arm connection to each quadrant, and means forretracting each retraction arm.
 5. Apparatus according to claim 1 inwhich each quadrant includes an upstanding end wall, an upstanding sidewall which meets the end wall to form an upright corner of the box, anda top panel above the side wall and end wall.
 6. Apparatus according toclaim 5 in which each wall retracting means comprises a separateelongated retraction arm connected to the upright corner of eachquadrant, and means for retracting each arm.
 7. Apparatus according toclaim 5 in which the retraction arms comprise a spider arrangementcrossing at the central axis of the interior of the box, each arm beingmounted to swivel about a horizontal axis, and in which the retractionarms are located in the upper interior portion of the box, and a secondset of retraction arms, each of which arms is connected to an uprightcorner of a respective quadrant, the arms in the second set being in aspider arrangement so that they cross at the central axis of theinterior of the box, and are disposed in the lower interior portion ofthe box, and including an extendable and contractable, verticallyextending arm disposed on the central axis of the interior of the boxand connected between the first and second sets of spiders, wherebyextension and contraction of the vertical arm pulls the upper and lowerspiders inwardly to retract the quadrants of the inner core. 8.Apparatus according to claim 1 in which each wall section is mounted ona separate set of elongated movable supports.
 9. A retractable castingcore for use with an outer form in the casting of generally hollowconcrete products, the casting core comprising wall-forming means havingan outer surface for forming the contour of a hollowed three-dimensionalinterior of a concrete casting, the wall-forming means having a sideportion which forms a closed mold surface and is defined by intersectingfirst and second planes, and a top portion forming a mold surface whichis integral with the side portion and is defined by a third plane whichintersects the first and second planes so the combined side portion andtop portion of the wall-forming means provide a continuousthree-dimensional mold surface, the top and side portions beingseparated into wall sections cooperating with each other to form thecontour of the concrete casting interior, the wall sections cooperatingto form a hollowed interior area of the retractable casting core, acompressible elastomeric joint seal between the wall sections, and meansin the hollowed interior area of the casting core for applying a forceto retract each of the wall sections inwardly away from the interior ofthe concrete casting, the wall retracting means directing a component ofits retracting force in a direction transverse to the joint seal whichborders each wall section to compress the seal to allow the wallsections to move toward each other as they move inwardly from theintErior of the casting.
 10. Apparatus according to claim 9 in which thewall-forming means is shaped as a hollowed rectangular box, with oneopen end for access to a hollow interior of the box, and in which thebox is separated substantially symmetrically into four quadrants, thejoint seal being aligned with each line of separation between thequadrants.
 11. Apparatus according to claim 10 in which the wallretracting means comprises at least one elongated retraction armconnected to each quadrant, and means for retracting each retractionarm.
 12. Apparatus according to claim 10 in which the wall-forming meansis engaged with the joint seal to direct a component of its retractingforce in a direction eccentric to the centroid of the seal such that theseal is substantially prevented from bulging beyond the outer surface ofthe quadrants.
 13. A retractable casting core for use with an outer formin a concrete mold assembly, the retractable casting core comprisingwall-forming means for providing an outer surface to form the contour ofa hollowed three-dimensional interior of a concrete casting, thewall-forming means being divided into a plurality of separate wallsections having cooperating outer surfaces which form thethree-dimensional contour of the concrete casting interior, the wallsections cooperating to form a hollowed interior portion of the castingcore, the separate wall sections being spaced apart from one another todefine a plurality of lines of separation spaced around the wall-formingmeans, a compressible elastomeric joint seal disposed in the lines ofseparation between the separate wall sections, and means in the hollowedinterior portion of the casting core for applying a retracting force tothe wall sections to move each wall section relative to the other wallsections inwardly toward the interior of the casting core and away fromthe casting, the wall retracting means directing a component of itsretracting force in a direction transverse to the joint seal in eachlines of separation between the wall sections to compress the joint sealto allow the wall sections to move toward each other as they moveinwardly from the interior of the casting.
 14. Apparatus according toclaim 13 in which the retracting means also directs the component of itsretracting force eccentric to the centroid of the seal such that theseal is substantially prevented from bulging beyond the outer surface ofthe wall sections.
 15. Apparatus according to claim 13 in which the wallsections are symmetrically arranged around the retractable casting core,and in which the retracting means retract the wall sections in unison.16. Apparatus according to claim 15 in which at least one elongatedretracting arm is connected to each wall section, and including meansfor retracting the retracting arms in unison.